Dewaxing mineral hydrocarbon oils



- bility of the solid wax in the oil.

Patented July 14, 1936;

UNITED STATES PATENT OFFICE to Shell Development Company, San 0alii., acorporation of Delaware Francisco,

No Drawing. Application A sust 17, 1935, Serial No. 38,717

18 Claims. 01'. 196-19) This invention relates to a process forseparating from mineral oils various waxy substances occurring therein.More particularly it pertains to a diluent for decreasing the viscosityof the oil and the solubility of the wax, whereby the wax and oil may bereadily separated when the oilsolvent mixture is chilled to solidify thewax.

Mineral oils, such, as petroleum hydrocarbon products and tars,naturally contain varying amounts of waxy paraihns or petrolatum, forconvenience hereinafter designated as waxes, which at normal or elevatedtemperatures are dissolved in the oil or are present in the liquidstate. but which tend to solidify or become very viscous at lowtemperatures, causing the oil to resist flow or to have a cloudyappearance.

The removal of wax from oil, and more particularly the removal ofmineral wax from mineral oil, has heretofore been accomplished bydiluting the waxy oil with a suitable diluent or diluent mixture,chilling the solution so formed to precipitate or solidify the wax, andseparating the solidified wax by some suitable means, such as filterpressing, centrifuging, or cold settling. The functionof the diluent wasto reduce the viscosity of the chilled mixture, whereby the separationof the wax was facilitated. I

' More recently it was proposed to improve the separation of the wax byemploying diluents or diluent mixtures which exercise a selectivesolvent action between the solid wax and the oil. For example, it'isknown to effect the separation of these waxes from hydrocarbon oils bydiluting the oil with mixtures of two liquids, one of which is a goodsolvent for hydrocarbons, and the other a poor solvent for solid param'nwax. Thus, a mixture of benzol and acetone has been used for dewaxinglubricating oils.

In such selective dewaxing mixtures the function of the selectivesolvent is to lower the solu- These selective solvents are, however, notsuiiiciently miscible with the oil at the dewaxing temperature, and itis often necessary to add another liquid which is miscible with the oiland with the selective solvent. This latter liquid is commonly known asthe solubility enhancing agent.

According to the present invention'it was found that particularly goodresults are obtained by dewaxing mineral oils in the presence of aselective dewaxing mixture containing low boiling hydrocarbon oilextract or recycled kerosene extract as the solubility enhancing agent.This extract may be obtained by extracting a low boiling hydrocarbondistillate, which may, for. exam-.

' as examples:

ple, be the portion of petroleum oils which is commonly known askerosene distillate, and which boils substantially within the range 150C. to 300 0., with a selective solvent for aromatics, i. e., with asolvent having the selective solvent characteristics of liquid sulfurdioxide. any solvent of this type may be used, particularly thefollowing, which are disclosed here merely Furfural (furfuraldehyde)nitrobenzene, pp dichlorethyl ether, cresol, and phenol. The term"kerosene" as used in the present specification and claims is used todesignate any hydrocarbon oil distillate boiling substantially between150 C. and 300 (3., although its actual boiling temperature rangeincludes but a portion of the stated range, and might for this reason beknown to the art by other names.

The hydrocarbon extract may be obtained by any process which iseffective in subjecting a hydrocarbon distillate to the extractiveaction of such a selective solvent. For example, a kerosene or lowerboiling oil distillate may be mixed with the solvent in an agitator ormixer, the resulting mixture allowed to stratify into two liquid layers,the layers separated, and the solvent layer or extract phase distilledor otherwise treated to separate it into solvent and hydrocarbonportions. This treatment may be conducted also in a packed tower, or ina multi-stage countercurrent' treater, as is well known in the art.

The kerosene or similar hydrocarbon distillate extract may also beproduced incidentally to the extraction of another hydrocarbon fraction.For example, in the extraction of lubricating oil, gas oil, Diesel fuel,or gasoline, kerosene distillate is sometimes mixed with the oil orintroduced in some other manner into the extraction zone to improve theextraction. In such extractions the produced extract will be a mixtureor a solution of the aromatic portions of both the kerosene and theparticular oil. The kerosene extract may be recovered from such extractsby simple or fractional distillation.

In such extraction processes employing low boiling hydrocarbondistillate or kerosene diluents, the hydrocarbon distillate may bepartially or entirely replaced by a hydrocarbon distillate extract,-derived from the same process (asby recycling a portion of thedistillate extract recovered as described in the preceding paragraphfrom a prior operation) or from a separate extraction operation. In suchprocesses which employ hydrocarbon distillate extract as a diluent, .thedistillate extract which is recovered from the extract phase will besubstantially richer in aromatic hydrocarbons, and will be more suitablefor use as the solubility enhancing agent, and is in the presentspecification and claims designated as recycled hydrocarbon extract.Although this recycled hydrocarbon extract is most conveniently producedin conjunction with the extraction of another hydrocarbon oil, it shouldbe noted .that it may also be produced by repeatedly extractinghydrocarbon distillate without the simultaneous extraction of otherhydrocarbon fractions, to obtain a highly aromatic extract. The termrecycled hydrocarbon extract is, therefore, to be taken to include anyhydrocarbon distillate extract which has been subjected to repeatedtreatments which concentrate its aromatic components, as defined below.

In general, it was found that the hydrocarbon distillate or keroseneextract to be employed as the solubility enhancing agent should possessthe following properties:

Boiling within the range 150 C. to 300 C. Gravity from A. P. 1... 8 to32 Total aromatics, by volume 60-100% Materlally improved results, are,however, obtained by using recycled kerosene extract. Such extractsshould have the following properties:

Boiling within the range 180 C. to 300 C. Gravity from ....A. P. I.-- 8to 25 Total aromatics, by volume 90-l00% Although I have indicated 180C. as the lower limit of the boiling range of my preferred recycledkerosene extract, it should be noted that my invention may also bepracticed with similar distillates having even lower initial boilingpoints, particularly when operating at lower dewaxing temperatures. Forexample, a recycled distillate with an initial boiling point of 150 C.may be suitable.

The selective solvent component which is used in my dewaxing mixturesmay be any polar compound which has the property of creating a conditionin the oil-wax-solvent system under which the wax has-a minimumsolubility in the liquid phases containing the oil. Among suchcompounds, may be mentioned the following: Sym- 'metrical andunsymmetrical aliphatic ketones,

aliphatic esters, aliphatic acids, hydroxy or ketoaliphatic acids,anhydrides of aliphatic acids, aliphatic alcohols, aliphatic carbonates,preferably containing not more than five carbon atoms in the molecule,as well as oxy-cyclic and nitrocyclic compounds, and halogen substitutedoxyaliphatic compounds. Specific examples of these groups are: Acetone,ethyl methyl ketone, diacetone alcohol, methyl formate, methyl acetate,ethyl acetate, acetic acid, butyric acid, lactic acid, acetic anhydride,methyl carbonate, ethyl 'formate, butyl alcohol, quinoline,iso-quinoline,

pyrrol, pp dichloroethyl ether, chloracetic acid, triethanol amine andaniline. Although I have enumerated a number of selective solvents whichmay be used with the hydrocarbon distillate extract in my dewaxingmixture, my invention is not limited thereto, but may be employed inconnection with other analogousselective solvents.

The constituents of the dewaxing mixture may be mixed in any desiredproportion, depending upon the amount of wax to be separated, upon thedilution ratio, and upon the separation temperature. It is essentialthat the mixture have a high solvent power for the liquid hydrocarbonsand a low solvent power for the solid hydrocarbons at the temperature atwhich the separation of the solid from the liquid hydrocarbons occurs.The low solubility selective solvents, of which the ketones and thequinolines form the preferred group, are effective for separating solidand liquid oil components, due to the difference in solubility of suchoil components in these solvents, but this action is limited by theirlow solubility in the oil at the low or moderate temperatures of thedewaxing operation. The hydrocarbon extract increases the solubility ofthe oily components, and aids the action of the selective solvents, aswill be seen from the examples hereinafter presented. Under certaincondition the hydrocarbon extract, has the further effect of reducingthe viscosity of the oil to aid in the separation of the liquid andsolid phases.

Suitablemixtures may, for example, consist of 50 parts of hydrocarbonextract, or recycled kerosene extract, and 50 parts of acetone orequivalent selective solvent, although 75/25 or 25/75 or other ratiosmay be employed, according as the nature of the oil is more parafllnicor more aromatic, and according as the other factors, heretoforediscussed, affect the solvent characteristics. It will, in general, bemore advantageous to use the minimum quantity of extract which isrequired to cause the dewaxing diluent and the oil to form a homogeneousliquid phase, at the temperature at which the separation occurs,although it is possible to use even smaller amounts of extract, therebypermitting 'two liquid phases to be formed in the system. Actualdewaxing with selective solvent mixtures has shown that most efficientdewaxing takes place at or near the composition of the dewaxing diluentwhich corresponds to the transition between the one liquid phase and thetwo liquid phase conditions. Eflicient is used here as implying mostdesirable combinations of pour point and yield. When largerconcentrations of solubility enhancing agent are employed in thedewaxing mixture, oil yields are higher, but the pour points are usuallyonly slightly below the dewaxing temperature. When smallerconcentrations of solubility enhancing agent are used, yields drop offvery sharply, and the pour point may be as much as 25 F. below thetemperature at which the solid wax is separated from the oil. By workingwith compositions which produce at the dewaxing temperature a singleliquid phase, but are near the two liquid phase composition, a betteryield may be obtained with but a small sacrifice of the pour point,which is often between F. and 10 F. below the separation temperature.With these eifects in mind it becomes possible to operate so as to causeeither a high yield, or a very low pour point, or any desiredintermediate result, and

to determine the proper ratio empirically in each particular case.

It is often desirable to use a eutectic mixture of these constituents.This is of particular advantage when dewaxing at very low temperatures.It was found that hydrocarbon extract and recycled hydrocarbon extractwere distinctly superior to benzol in operations of this type becausethe extracts remained liquid at temperatures. at which benzol, when usedin a corresponding concentration, crystallized. It was found thatexcellent results were obtained when dewaxing at extremely lowtemperatures, such as 20 C. and lower, but using hydrocarbon ex-.

tracts and particularly recycled hydrocarbon extracts boiling between150 C. and 240 C.

2,047,826 Thedilution ratio, i. e., the volume ratio of oil to dewaxingmixture is determined by the viscosity needed at the filtration orsettling temperature and may vary with the character of the oil and theviscosity of the diluents employed, but can be readily determined bythose skilled in the art.

The process may be operated by dissolving the wax-bearing oil, such asparafllnous petroleum residues, paraflinous lubricating oils, lignitetars, shale oils, low temperature tars, and fuel oils in the selectivedewaxing mixture, after which the paraiiin wax is caused to separate outin a crystalline or amorphous state at a lower temperature, such as, forexample, 0 0., depending on the desired pour point of the oil and thedesired melting point of the wax. Theseparation may be carried out inanydesired manner, al-

though I have found filtration methods to be' the best for my solvents.centrifuging and cold settling may, however, often be employed,especially when the specific gravity of the selective solvent is such asto cause a sufiicient difierence between the densities of the oil phaseand the precipitated wax crystals. I have found that my dewaxing mixtureis efiective to cause the pour point of the dewaxed oil to be oftensomewhat below the temperature at which the wax is separated. After theseparation of the wax the dewaxing solvents may be removed from the oiland from the "wax by ordinary or vacuum distillation, or by any othermethod, such as washing with a suitable selective solvent, such as ethylalcohol, to dissolve the selective solvent .component of the dewaxingmixture, and then distilling'the oil or wax to recover the kerosene orsimilar distillate extract and/or other selective solvent remainingtherein. The dewaxing may be conducted either according to a continuousor a batch method.

It is desirable, but not essential, to produce a homogeneous oil-solventsystem before chilling the oil to precipitate the wax. To achieve this,the dewaxing diluent may be added to the oil at an elevated temperature,or the mixture of oil and diluent may, after mixing, be heated. It is,

moreover, often advantageous to heat the mixture to a temperaturebetween 65 0. and 100 C. before chilling to condition the wax,and'thereby improve the filter rate.

Under certain conditions, as when a moderately high pour point ispermissible, and/or when,

in a multiple stage process, it is desired to obtain high melting wax inthe first stage, the precipitation of the wax may be eifected attemperatures which are the same as or only slightly below normal. Inthis manner a relatively highmelting wax may be produced. The oilfiltrate may, after further addition of dewaxing diluent, be furtherchilled to separate additional quantities of wax. g

It is not necessary to mix all of the components of the solvent mixturebefore dissolving them in the oil. Thus, the hydrocarbon extract orrecycled hydrocarbon extract may be added first, or may be present inthe oil as aresult of its use as a diluent in a prior solventextraction. step, and the requisite amount of the selective solvent or asolution of low boiling hydrocarbon distillate extract having a highconcentration of the selective solvent may be added separately to theoil.

The effect of using low boiling hydrocarbon extract as the solubilityenhancing agent will be seen from the following examples:

Example I.-Seve'ral portions of a lubricating oil distillate derivedfrom a-Ventura crude, and

.having a pour point of 95 were each diluted with four parts by volumeof solvent mixtures of the composition shown in the following table,

heated for half an hour to raise the temperature to between C. and C.,chilled for about ten hours to lower the temperature to 0 (3., andfiltered at temperatures between 0 C. and 1 C. The results are shown inthe table:

Diluent Filtration Dewaxed oil 1% R cl d Y 1a P o. ecy 0 1e our Acetonekerosene X 5 g volume point extract percent F.

Example Ill-Several portions of the same Venture. distillate weresimilarly treated, except that the chilling was more drastic, so that in8 /2 hours the mixture was chilled to 20 0., and the chilled mixture wasfiltered at temperatures between -l9 C. and 20 C. The results are shownin the following table:

Diluent Filtration Dewaxed oil 1 R 1 d Y ld P o. ecyc e 1e our Acetonekerosene X 5 2 3 volume point extract percent F.

My invention is not restricted to the operating conditions, nor to theconcentrations and dilution ratios, nor to the specific selectivesolvent de scribed in the preceding examples, because it may bepracticed under widely varying conditions and with many other selectivesolvents.

I claim as my invention:

1. A process for dewaxing oil by mixing waxbearing mineral oil with aliquid dewaxing-agent having a high solvent power for the oilycomponents of the wax-bearing oil but low solubility for its waxycomponents, chilling the resulting mixture to precipitate waxycomponents, and separating the precipitated wax from the liquid,characterized by the use of hydrocarbon extract boiling substantiallybelow 300 C. and having an A. P. I. gravity not substantially over 32,and a selective solvent having a low solvent power for oil and misciblewith kerosene extract as the dewaxing agent.

2. A process for dewaxing oil by mixing waxbearing mineral oil with aliquid dewaxing agent having a high solvent power for the oilycomponents of the wax-bearing oil but low solubility for its waxycomponents, chilling the resulting mixture to precipitate waxycomponents, and separating the precipitated wax from the liquid,characterized by the use of recycled hydrocarhon extract boilingsubstantially below 300 C. and having an A. P. I. gravity notsubstantially over 25", and a selective solvent having a low solventpower for oil and miscible with recycled kerosene extract, as thedewaxing agent.

3. A process for dewaxing oil'by mixing waxbearing mineral oil with aliquid dewaxing agent having a high solvent power for the oil componentsof the wax-bearing oil but low solubility for its waxy components,chilling the resulting mixture to precipitate waxy components, andseparating the precipitated wax from the liquid, characterized by theuse of kerosene extract having a boiling range substantially between 150C. and 300 C. and an A. P. I. gravity not substantially over 32, and aselective solvent from the group consisting of iurfural, aniline,nitrocyclic compounds, aliphatic acids, hydroxy aliphatic acids,aliphatic esters, aliphatic alcohols, aliphatic ketones, and aliphaticcarbonates, said aliphatic compounds having less than six carbon atomsin the molecules, as the dewaxing agent.

4. A process for dewaxing oil by mixing waxbearing mineral oil with aliquid dewaxing agent having a high solvent power for the oilycomponents of the wax-bearing oil but low'solubility forits waxycomponents, chilling the resulting mixture to precipitate waxycomponents, and sepmating the precipitated wax from the liquid,characterized by the use of kerosene extract having aboiling rangesubstantially between 150 and 300 C. and an A. P. I. gravity notsubstantially over 32, and an aliphatic ketone having not more than fivecarbon atoms in the molecule,

as the dewaxing agent.

5. A process for dewaxing oil by mixing waxbearing mineral oil with aliquid dewaxing agent having a high solvent power for the oil componentsof the wax-bearing oil but low solubility for its waxy components,chilling the resulting mixture to precipitate waxy components, andseparating the precipitated wax from the liquid, characterized'by theuse of recycled kerosene extract having a; boiling range substantiallybetween 150 and 300 C. and an A. P. I. gravity not substantially over25, and an aliphatic ketone having not more than five carbon atoms inthe molecule, as the dewaxing agent.

6. A process for dewaxing oil by mixing waxbearing mineral oil with aliquid dewaxing agent having a high solvent power for the oil componentsof the wax-bearing oil but lowsolubility for its waxy components,chilling the resulting mixture to precipitate waxy components, andseparating the precipitated wax from the liquid, characterized by theuse of kerosene extract having a boiling range substantially between 150and 300 C. and an A. P. I. gravity not substantially over 32", andacetone, as the dewaxing agent.

'7. A process of dewaxing mineral lubricating oil comprising the stepsof mixing a wax-bearing mineral oil with an effective quantity of asubstance from the group consisting of furfural, aniline, nitrocycliccompounds, aliphatic acids, hydroxy aliphatic acids, aliphatic esters,aliphatic alcohols, aliphatic ketones, and aliphatic carbonates, saidaliphatic compounds having less than six carbon atoms in the molecules,precipitating wax from the resulting mixture at a suitable temperatureat which at least a portion of the wax is solidified in the presence ofkerosene extract having a boiling range substantially between 150 and300 C., and an A. P. I. gravity not substantially over 32, the quantityof said kerosene extract being s'ufllcient to prevent the separation ofsubstantial amounts of oil from the oil-solvent mixture during theprecipitation, and mechanically separating the precipitated wax from thesolution.

8. A process of dewaxing mineral lubricating oil comprising the steps'ofmixing a wax-bearing mineral oil with an effective quantity of asubstance from the group consisting of furfural, aniline, nitrocycliccompounds, aliphatic acids, hydroxy aliphatic acids, aliphatic esters,aliphatic alcohols, aliphatic ketones, and aliphatic carbonates, saidaliphatic compounds having less than six carbon atoms in the molecule,precipitating wax from the resulting mixture at a suitable temperatureat which at least a portion of the wax is solidified, in the presence ofrecycled kerosene extract having a boiling range substantially between150 and 300 C., and an A. P. I. gravity not substantially over 25, thequantity of said recycled kerosene extract being sufilcient to preventthe separation of substantial amounts of oil fromthe oil-solvent mixtureduring the precipitation, and mechanically separating the precipitatedwax from the solution.

9. A process of dewaxing mineral lubricating oil comprising the step ofmixing a wax-bearing mineral oil with an effective quantity of analiphatic ketone having not more than 5 carbon atoms in the molecule,precipitating wax from the resulting mixture at a suitable temperatureat which at least a portion of the wax is solidified, in the presence ofkerosene extract having a boiling range substantially between 150 and300 C., and an A. P. I. gravity not substantially over 32, the quantityof said kerosene extract being suflicient to prevent the separation ofsubstantial amounts of oil from the oil-solvent mixture during theprecipitation, and mechanically separating the precipitated wax from thesolution.

10. A process for dewaxing mineral oil, comprising the steps of mixing amineral wax-bearing oil with a selective solvent having a low solventpower for oil and being miscible with kerosene extract, subsequentlydescribed, precipitating wax from the resulting mixture at a lowtemperature in the presence of a quantity of kerosene extract having aboiling range substantially between 150 and 300 C., and an A. P. I.gravity not substantially over 32, and mechanically separating theprecipitated wax from the solution, the quantity of kerosene extractbeing suflicient to cause the oil and -diluents to exist as a singleliquid phase at the temperature of said separation.

11. A process for dewaxing mineral oil, comprising the steps of mixing amineral wax-bearing oil with a selective solvent having a low solventpower for oil and being miscible with recycled keroseneextract,subsequently described, precipiting wax from the resulting mixture at alow temperature in the presence of a quantity of recycled keroseneextract having a boiling range substantially between 150 and 300 C., andan A. P. I. gravity not substantially over 25, and mechanicallyseparating the precipitated wax from the solution, the quantity ofrecycled kerosene extract being suflicient to cause the oil and diluentsto exist as a single liquid phase at the temperature of said separation.

. 12. The process according to claim 11 in which the quantity ofrecycled kerosene extract is not substantially greater than required tocause the oil and the diluents to exist as'a single liquid phase.

13. A process for producing low pour point mineral oils, comprising thesteps of mixing a mineral wax-bearing oil with a selective solventtially between and 240 C., and an A. P. I. 73

Ill

acaaeec I; l

gravity not substantially over 25", chilling the resulting mixture to atemperature below -20 C. to precipitate wax from the solution, andmechanically separating the precipitated wax from the solution at atemperature below --20 C.

14. The process according to claim 13 in which the selective solvent isacetone.

15. A process for dewaxing mineral oil, comprising the steps of mixing amineral wax-bearing oil with a selective solvent having a low solventpower for oil and being miscible with kerosene extract having a boilingrange substantially between 150 and 300 (1., and an A. P. I. gravity notsubstantially over 32, precipitating wax from the mixture in thepresence of said kerosene'extract at a temperature at which the mixtureof said selective solvent, kerosene extract, and oil remains liquid, andat which benzene crystallizes from a mixture of the same composition butcontaining benzene instead of kerosene extract, and

mechanically separating the precipitated wax from the solution of oil,selective solvent and kerosene extract.

16. A process for dewaxing mineral oil, comprising the steps of mixing amineral wax-bearing oil with a selective solvent having a low solventpower for oil and being miscible with recycled kerosene extract having aboiling range substantially between 150 C. and 300 C., and an A. P. I.

gravity not substantially over 25, precipitating from the solution ofoil, selective solvent and recycled kerosene extract. 17. A process fordewaxing mineral oil, comprising the steps of mixing a mineralwax-bearing oil with a selective solvent having a low solvent power foroil and being miscible with recycled hydrocarbon extract boilingsubstantially below 240 C., and having an A. P. I. gravity notsubstantially over 25, precipitating wax from the mixture inthe presenceof said recycled kerosene extract at a temperature at which the mixtureof said selective solvent, recycled kerosene extract, and oil remainsliquid, and at which benzene crystallizes from a mixture of the saniecomposition but containing benzene instead of recycled kerosene extract,and mechanically separating the precipitated wax from the solution ofoil, selective solvent and recycled kerosene extract.

18. A process for dewaxing mineral oil, comprising the steps of mixing amineral wax-bearing oil with a selective solvent having a low solventpower for oil and being miscible with recycled kerosene extract having aboiling range substantially between 150 and 240 C., and having an 2 A.P. I. gravity not substantially over precipitating wax from the mixturein the plesence of said recycled kerosene extract at a temperature atwhich the mixturepf said selective solvent, recycled kerosene extract,and oil remains liquid, and at which benzene crystallizes from a mixtureofthe same composition but containing benzene instead of recycledkerosene extract, and mechanically separating the precipitated wax fromthe solution of oil, selective solvent and recycled kerosene extract.

CHEVER M. KELLOGG.

